— Are there any flowers _______ the tree.— No. But there are many birds _________ it.
A:in, on
B:in, in
C:on, in
D:on, on
-What are you looking for?
-I'm looking for the watch ___________ I bought yesterday.
杂交水稻之父﹣﹣袁隆平在育种中实质上利用了( )